Since you are mostly doing it in studio (face shot) with lots of artificial lights (flash, screens) available, you won't need high ISO desperately. And if it is the case, any modern full frame will work. You said you have canon lenses already, so why switch to Nikon ? If you have such amount of money then buy 5D mk 3 or even 1DX instead. No one can beat 1DX in any situation.
I wish a 1 inch sensor with that fast lens on next model. It would be better than sony RX1. Panasonic, please hear me. :)